Fix global rateCollector init multiple times (#23703)

Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>

internal/datanode/data_node.go

@@ -84,9 +84,6 @@ var _ types.DataNode = (*DataNode)(nil)
 // Params from config.yaml
 var Params *paramtable.ComponentParam = paramtable.Get()
 
-// rateCol is global rateCollector in DataNode.
-var rateCol *rateCollector
-
 // DataNode communicates with outside services and unioun all
 // services in datanode package.
 //
@@ -220,8 +217,7 @@ func (node *DataNode) initSession() error {
 
 // initRateCollector creates and starts rateCollector in QueryNode.
 func (node *DataNode) initRateCollector() error {
-	var err error
-	rateCol, err = newRateCollector()
+	err := initGlobalRateCollector()
 	if err != nil {
 		return err
 	}

internal/datanode/rate_collector.go

@@ -23,6 +23,10 @@ import (
 	"github.com/milvus-io/milvus/pkg/util/typeutil"
 )
 
+// rateCol is global rateCollector in DataNode.
+var rateCol *rateCollector
+var initOnce sync.Once
+
 // rateCollector helps to collect and calculate values (like rate, timeTick and etc...).
 type rateCollector struct {
 	*ratelimitutil.RateCollector
@@ -31,6 +35,14 @@ type rateCollector struct {
 	flowGraphTt   map[string]Timestamp
 }
 
+func initGlobalRateCollector() error {
+	var err error
+	initOnce.Do(func() {
+		rateCol, err = newRateCollector()
+	})
+	return err
+}
+
 // newRateCollector returns a new rateCollector.
 func newRateCollector() (*rateCollector, error) {
 	rc, err := ratelimitutil.NewRateCollector(ratelimitutil.DefaultWindow, ratelimitutil.DefaultGranularity)